The present invention is concerned with a novel process for preparing 5-cyano-4-methyl-oxazole, which is an important intermediate in the manufacture of pyridoxine (vitamin B.sub.6).
This oxazole derivative has, before now, been manufactured by reacting 5-carbamoyl-4-methyl-oxazole with phosphorus pentoxide while heating. However, this process is associated with certain disadvantages, for example, a relatively low yield, attributable to carbonization which occurs very readily.
An improvement for this process comprises carrying out the reaction of the 5-carbamoyl-4-methyl-oxazole with the phosphorus pentoxide in the presence of a solvent, namely quinoline (see U.S. Pat. No. 3,222,374). This process also has disadvantages, particularly, instability observed under reaction conditions, a disagreeable odor, and detrimental effects on health of quinoline. Further, the procedures for the regeneration of quinoline and for converting products which are formed from the required phosphorus pentoxide into ecologically harmless products are costly and burdened with technological problems. Moreover, both quinoline and phosphorus pentoxide are expensive and scarce raw materials.
Another process for the manufacture of 5-cyano-4-methyloxazole comprises reacting 5-carbamoyl-4-methyl-oxazole with a lower alkanecarboxylic acid anhydride and subjecting the reaction mixture or the 5-(N-lower alkanoyl-carbamoyl)-4-methyl-oxazole isolated therefrom to pyrolysis. The final pyrolytic step has, however, certain disadvantages, such as, the necessity for working at high temperatures, problems with the materials from which the reactor is constructed, and the formation of byproducts which are difficult to recycle.